Stability of the Si-H bonds on the hydrogen-terminated Si(1 1 1) surface has been investigated by sum frequency generation (SFG) spectroscopy in air at room temperature. The SFG observation showed that the Si(1 1 1) surface is terminated by a monolayer of monohydride (Si-H) after etching in a concentrated ammonium fluoride (NH4F) solution. The number of Si-H bonds decreased with laser irradiation time and the abstraction rate of hydrogen atoms on Si increased with the increase of input energy of `visible' light. The Si-H bond under irradiation at 1064 nm light was more stable than that at 532 nm light with a given intensity. A small amount of water in air severely lowered the stability of Si-H bond because of a photoelectrochemical reaction under laser irradiation.
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